1. Field of the Invention
The present invention relates a disk sub-system composed of multiple disk units and a disk controller that controls these, particularly relates to a disk controller composing the disk subsystem by plural disk controllers and a method of controlling a cache memory in the disk controller.
2. Description of the Related Art
A disk controller (hereinafter called DKC) stores and reads data in/from multiple disk units (hereinafter called disk drives or merely drives). The disk drives and DKC are generically called a disk subsystem. FIG. 17 shows the configuration of such a conventional type disk sub-system.
In the conventional type disk sub-system, two host computers 0 are respectively connected to two disk sub-systems 1 via a channel 2. A logical disk 7 is a memory area which the host computer 0 recognizes. The host computer 0 instructs to refer to data at a specific address of the logical disk 7 and to request the update of the data via the channel 2. For the channel 2, there are a fiber channel, SCSI and others.
The disk sub-system 1 is roughly composed of DKC 10 and plural drives 17. DKC 10 and the plural drives 17 are connected via a drive interface 16. For the drive interface 16, a fiber channel, SCSI and others are used.
DKC 10 is roughly composed of a channel controller 11 that controls channels, a disk drive controller 14 that controls drives, a control memory 12 that stores the control information 3 of DKC, a cache memory part 13 that stores read data 5 and update data 6 and further, a connection mechanism 15 that mutually connects each component. For the connection mechanism 15, a bus, an interconnection network and others are used.
DKC 10 executes the reference of data and update processing according to the instruction of the host computer 0. Such a conventional type disk subsystem is disclosed in Japanese published unexamined patent application No. Hei 12-99281 for example.
In recent computer environment as represented by the explosive popularization of the Internet, storage capacity used by a user rapidly increases. As a result, the management cost of daily increasing data also continues to increase and the reduction of the management cost is an important problem. Also, a storage area network (hereinafter called SAN) for centralizing disk subsystems heretofore connected each server and as a result distributed, attracts attention. FIG. 18 shows a conventional type example of disk subsystems in SAN environment. Plural sub-systems are connected to the host computers 0 via SAN-SW 11. One disk sub-system is composed of only one disk controller.
As described above, the further increase of storage capacity and the increase of the number of connected channels are demanded for a disk subsystem by the change of environment surrounding the disk subsystem.
It is conceivable in consideration of such a background that a disk sub-system heretofore composed of one DKC is composed of plural DKCs. Hereby, for a disk subsystem, larger storage capacity and the more number of connected channels can be provided.
For a general method of composing plural DKCs, it is conceivable to compose DKC by clusters. However, in this case, there is a problem that it is difficult to share data between DKCs. To solve this problem, it can be realized to share data by enabling the mutual access of data between DKCs using connection means between DKCs.